Currently, standards committee IEEE 802.21 conducts intensive research into the international standards associated with media independent handover (MIH) between heterogeneous networks. MIH provides not only a seamless handover but also a service continuity between the heterogeneous networks, resulting in greater convenience for a user who carries a mobile terminal. IEEE 802.21 defines a variety of functions (e.g., an MIH function, an event service, a command service, and an information service (IS) function) as basic requirements.
A mobile terminal is indicative of a multi-mode node for supporting at least two interface types. For example, the multi-mode node can support a variety of interface types, such as a wired interface type (also called a wire-line interface type) such as the Ethernet based on an IEEE 802.3 standard specification, a wireless interface type based on IEEE 802.XX standard specifications (e.g., a broadband wireless access network system, a wireless LAN, a wired LAN, and a cellular system interface), and other interface types defined by a cellular standardization organization (e.g., 3GPP or 3GPP2).
A general Media Independent Handover Function (MIHF) reference model is depicted in FIG. 1. In the figure, MIHF architecture for interaction with other layers and with the remote MIHG is illustrated. In order for the MIHF to provide asynchronous and synchronous services to lower layers and higher layers, Service Access Points (SAPs) such as MIH_MGMT_SAP, MIH_SME_SAP and MIH_SAP along with primitives are defined. MIH_MGMT_SAP defines the interface between the MIHF and the management plane (Management Entity) of different network interfaces and is used for transporting MIH protocol messages between the MIHF and local link layer entities as well as peer MIHF entities. MIH_SAP defines the interface between the MIHF and higher layer entities such as device manager, handover policy control function, transport, layer 3 (L3) mobility management protocol, etc., and is used for MIH configuration and operation. MIH_SME_SAP defines the interface between the MIHF and the Station Management Entity or the Network Management System, and is used for MIG configuration and operation.
FIG. 2 is a structural diagram illustrating a multi-mode mobile terminal. Referring to FIG. 2, the multi-mode mobile terminal includes a physical (PHY) layer and a Medium Access Control (MAC) layer for individual modes, and locates a Media Independent Handover (MIH) layer under the IP layer.
Media Independent Handover (MIH) must be defined between IEEE 802-series interfaces, or must be defined between an IEEE 802-series interface and a non-802-series interface (e.g., 3GPP and 3GPP2). Also, a protocol for supporting mobility of upper layers such as a mobile IP and a Session Initiation Protocol (SIP) must be supported for a handover function and continuity of services.
The MIH function is located under the IP layer, and facilitates a handover process using input values (e.g., a trigger event and information associated with other networks) received from a second layer (Layer 2). The MIH function may include a plurality of input values based on both user policy and configuration which may affect the handover process. General interfaces among the mobile IP, a third layer (Layer 3) entity such as an SIP (Session Initiation Protocol), and the MIH layer are defined. In this case, the aforementioned interfaces provide the first layer (i.e., the physical layer), the second layer (i.e., the MAC layer), and mobility management information. The MIH function acquires information associated with a lower layer and a network using event and information service (IS) functions.
An upper layer includes an upper management entity for monitoring states and operations of various links contained in a mobile terminal, such that it performs a handover control function and a device manager function. In this case, the handover control function and the device manager may be located at different locations independent of each other, or the handover control function and the device manager may be included as the upper management entities in the upper layer.
A network structure for supporting a mobile IP includes a Home Agent (HA), a Foreign Agent (FA), and a Mobile Subscriber Station (MSS). A variety of functions are required to operate the mobile IP, i.e., an agent discovery function, a registration function, and a routing function.
The agent discovery function is indicative of a method for allowing a mobile terminal to determine whether the mobile terminal is connected to its own home network or a foreign network, such that the mobile terminal can recognize whether the mobile terminal itself has moved to another network.
According to the registration function, if the mobile terminal moves to another network, it transmits current location information to the home agent, and allows the mobile terminal to receive services from the home network without any change, in such a way that the registration function provides a highly adaptable mechanism.
The routing function defines a variety of functions required for properly routing a datagram transmitted/received to/from the mobile terminal when the mobile terminal is connected to or accesses a foreign network.
The mobile IP provides two registration procedures fore establishing a temporary address or Care of Address (CoA) when the mobile terminal moves to another subnet. For example, the two registration procedures are FA-CoA and co-located CoA.
If the FA-CoA is used, the CoA is supplied from a foreign agent (FA) via an agent advertisement message, and an IP address of the foreign agent (FA) is used as a temporary address (CoA). If the co-located CoA is used, the mobile terminal receives a temporary address (CoA) via a DHCP (Dynamic Host Configuration Protocol) server located at the foreign network.
The DHCP is indicative of a protocol which allows network managers to centrally manage/allocate necessary IP addresses in a network contained in their organization. When computer users gain access to the Internet in an organization, the IP address must be assigned to individual computers. When the network manager centrally manages/allocates the IP address, and a computer is connected to the Internet at other places outside of the network, the DHCP automatically transmits a new IP address.
The DHCP employs a rental (or lease) scheme for controlling a given IP address to be valid at a corresponding computer during a predetermined period of time only. A lease time may be changed according to an Internet access time required by a user at a specific location. The DHCP may also reduce the IP-address lease time when many more computers than available IP addresses are used, such that it can dynamically reconstruct a network.
If a system starts its operation, a plurality of clients request unique IP addresses for their systems from the DHCP server. If the clients receive their IP addresses from the DHCP server, the TCP/IP setup is initialized, and the clients communicate with other hosts using a TCP/IP protocol. The DHCP server answers an IP address lease request of a DHCP client, such that it maintains/manages the scope of allocatable IP addresses (e.g., 203.224.29.10˜203.224.29.100).
The following Table 1 shows a DHCP message format.
TABLE 108162431OPHTYPEHLENHOPSTRANSACTION IDENTIFIERSECONDS ELAPSEDFLAGSCLIENT IP ADDRESSYOUR IP ADDRESSSERVER IP ADDRESSROUTER IP ADDRESSCLIENT HARDWARE ADDRESS (16 OCTETS)...SERVER HOST NAME (64 OCTETS)...BOOT FILE NAME (128 OCTETS)...OPTIONS (VARIABLE)...
The following Table 2 shows various types and usages of the DHCP messages.
TABLE 2MessageUseDHCPDISCOVERClient broadcast to locate available servers.DHCPOFFERServer to client in response to DHCPDISCOVERwith offer of configuration parameters.DHCPREQUESTClient message to servers either (a) requestingoffered parameters from one server andimplicitly declining offers from all others,(b) confirming correctness of previouslyallocated address after, e.g., system reboot,or (c) extending the lease on a particularnetwork address.DHCPACKServer to client with configuration parameters,including committed network address.DHCPNAKServer to client indicating client's notion ofnetwork address is incorrect (e.g., client hasmoved to new subnet) or client's lease asexpiredDHCPDECLINEClient to server indicating network address isalready in use.DHCPRELEASEClient to server relinquishing network addressand canceling remaining lease.DHCPINFORMClient to server, asking only for localconfiguration parameters; client already hasexternally configured network address.
The principal components for mobile IPv6 system operations, and functions of individual principal components will hereinafter be given.
A mobile node (MN) is a host or router for switching its network access. A correspondent node (CN) is a host or router communicating with the mobile node (MN). The home agent (HA) acts as a router and has registration information of the mobile node (MN) obtained from routers contained in a home network. Accordingly, the home agent (HA) can transmit a datagram to a current position of the mobile node (MN) contained in a foreign network.
The temporary address or Care of Address (CoA) is indicative of an IP address connected to a mobile node when the mobile node moves to a foreign node or foreign agent (FA). The term “Binding” is indicative of a specific operation in which the mobile node matches the CoA registered in the home agent with a home address of a corresponding node. A “Binding Update (BU)” message is indicative of a message used when the mobile node itself informs the home agent (HA) and the correspondent node (CN) of a CoA of the mobile node. A “Binding Acknowledge (BACK)” message is indicative of a response message to the aforementioned “BU” message. A “Binding Request (BR)” message is indicative of a message for requesting the “BU” message when the correspondent node (CN) does not receive the “BU” message until a timer for the binding information of the mobile node expires.
The mobile node (MN) automatically constructs its location information while in motion using a neighbor discovery function and an address auto-configuration function. If a correspondent node (CN) stores the binding information, the correspondent node (CN) directly communicates with the mobile node without passing through the home agent in such a way that a Router Optimization is performed.
An IP address auto-configuration method is classified into two address auto-configuration methods such as a state-maintenance-type address auto-configuration method for acquiring an address using a server such as the DHCP server, and a non-state-type address auto-configuration method for controlling a host so that the mobile node can generate an address by itself.
The state-maintenance-type address auto-configuration method is adapted to assign one of a plurality of addresses capable of being assigned from the server to the host on the condition that the host requests an address from the DHCP server. The non-state-type address auto-configuration method combines the mobile node's interface ID information with either prefix information acquired from the router or well-known prefix information, such that the mobile node forms an address.
DHCPv6 is indicative of a DHCP protocol for the IPv6 system, and supports the state-maintenance-type address auto-configuration method. The DHCPv6 is indicative of a specific mechanism by which an IP address, various information (e.g., routing information), and a network resource management function are concentrated on a small number of DHCP servers, resulting in reduction of maintenance costs.
The DHCPv6 employs two multicast addresses, such as an “All_DHCP_Relay_Agents_and_Servers” address and an “All_DHCP_Servers” address.
The “All_DHCP_Relay_Agents_and_Servers” address is indicative of a link local multicast address used by the client, such that the client communicates with the agent contained in a link on the condition that a link local address of the agent is unknown. In this case, all servers and agents act as members of the above multicast group.
The “All_DHCP_Servers” address is indicative of a site local multicast address, which is used by a client or a relay when the client or the relay transmits a message to all servers or does not recognize unicast addresses of the servers, such that the client or the relay can communicate with the server. In order to allow the client to use the above-mentioned “All_DHCP_Servers” address, the client must have addresses of sufficient ranges at which the server arrives. In this case, all servers contained in a site act as members of the above-mentioned multicast group.
A variety of messages can be used for basic operations of the DHCPv6, for example, a “SOLICIT” message, an “ADVERTISE” message, a “REQUEST” message, a “REPLY” message, a “RENEW” message, and a “RELEASE” message.
The “SOLICIT” message is adapted for the client to recognize location information of the server, and is multitasked using the “All_DHCP_Servers” address. The “ADVERTISE” message is indicative of a response message to the “SOLICIT” message. If possible, the DHCP server answers the “SOLICIT” message. The “REQUEST” message is adapted to acquire constituent parameters equipped with an IP address from the server selected by the client, and is multitasked using the “All_DHCP_Relay_Agents_and_Servers” address. The “REPLY” message is indicative of a response message to the aforementioned “REQUEST”, “RENEW”, and “RELEASE” messages. The “RENEW” message is indicative of a message required when the client acquires an initially-allocated client address and the lifetime of the constituent parameters. The “RELEASE” message is indicative of a message required when the client returns at least one IP address to the server.
FIG. 3 shows an MIH structure and a transmission protocol. A heterogeneous network and a handover technique will hereinafter be described with reference to FIG. 3. Referring to FIG. 3, the MIH function is located under the IP layer, and facilitates a handover process using input values (e.g., a trigger event and information associated with other networks) received from a second layer (Layer 2).
The MIH function may include a plurality of input values based on both user policy and configuration which may affect the handover process. General interfaces among the mobile IP, a third layer (Layer 3) entity such as an SIP (Session Initiation Protocol), and the MIH layer are defined. In this case, the aforementioned interfaces provide the first layer (i.e., the physical layer), the second layer (i.e., the MAC layer), and mobility management information. The MIH function acquires information associated with a lower layer and a network using event and information service (IS) functions. Accordinglhy, the upper layer must include the MIH function for monitoring/controlling states of various links contained. Dotted lines of FIG. 3 are indicative of primitive information and an event trigger, for example.
FIG. 4 is a block diagram illustrating an event trigger. In order to quickly perform a handover function, a network layer must use information generated from a link layer, such that the network layer can quickly re-establish a connection state. The link layer event is adapted to predict the movement of a user, and helps a mobile terminal and a network to prepare the handover function.
Referring to FIG. 4, a trigger for the handover may be initiated from the physical (PHY) layer and the MAC layer. A source of the trigger may be determined to be a local stack or a remote stack. An event trigger provides state information of a current signal, state change information of another network, and future predicted change information. The event trigger also includes change information of the physical and MAC layers or attribute change information of a specific network.
The event types can be classified into a physical (PHY) layer event, a MAC layer event, a management event, a third layer (L3) event, and an application event, for example.
FIG. 5 shows triggers generated until a link setup process from a current access link to a new link is performed. Basic trigger events (i.e., “Link_Up” event, “Link_Down” event, “Link_Going_Down” event, “Link_Going_Up” event, “Link_Event_Rollback” event, “Link_Available” event, “Link_Parameters_Change” event, “IP_Renewal_Indication” event, and “IP_Renewal_Request” event, for example) will hereinafter be described with reference to FIG. 5.
A “Link_Up” event occurs when a second layer (L2) connection is established on a specific link interface and an upper layer is able to transmit third layer (L3) packets. In this case, it is determined that all L2 layers contained in a link have been completely configured. A source of the “Link_Up” event corresponds to a “Local MAC” and a “Remote MAC”. The following Table 3 shows parameters of the “Link_Up” event.
TABLE 3NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource at whichevent occursEventDestinationEVENT_LAYER_TYPEDestination to whichevent is to betransmittedMacMobileTerminalMAC AddressMAC address ofMobile TerminalMacOldAccessRouterMAC AddressMAC address of oldaccess routerMacNewAccessRouterMAC AddressMAC address ofnew access routerNetworkIdentifierMedia SpecificNetwork ID used fordetecting subnetchange
A “Link_Down” event occurs when the L2 connection is released on a specific interface and L3 packets cannot be transmitted to a destination. The source of the “Link_Down” event is indicative of a local MAC. The following Table 4 shows parameters of the “Link_Down” event.
TABLE 4NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource at whichevent occursEventDestinationEVENT_LAYER_TYPEDestination to whichevent is to betransmittedMacMobileTerminalMAC AddressMAC address ofMobile TerminalMacOldAccessRouterMAC AddressMAC address of oldaccess routerReasonCodeReason for releasedlink
A “Link_Going_Down” event occurs when it is expected that the L2 connection will enter a “Link_Down” state within a predetermined time, and may serve as a signal for initializing a handover procedure. A source of the “Link_Going_Down” corresponds to a “Local MAC” and a “Remote MAC”. The following Table 5 shows parameters of the “Link_Going_Down” event.
TABLE 5NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource at whichevent occursEventDestinationEVENT_LAYER_TYPEDestination to whichevent is to betransmittedMacMobileTerminalMAC AddressMAC address ofMobile TerminalMacOldAccessRouterMAC AddressMAC address of oldaccess routerMacNewAccessRouterMAC AddressMAC address ofnew access routerTimeIntervalTime in msecsPredictedLink_Downtime of linkConfidenceLevel%Link_Down levelpredicted at specifictimeUniqueEventIdentifierUse in eventrollback occurrence
A “Link_Going_Up” event occurs when it is expected that the L2 connection will enter a “Link_Up” state within a predetermined time, and is used when a long period of time is consumed to initialize a network. A source of the “Link_Going_Up” event corresponds to a “Local MAC” and a “Remote MAC”. The following Table 6 shows parameters of the “Link_Going_Up” event.
TABLE 6NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource at whichevent occursEventDestinationEVENT_LAYER_TYPEDestination towhich event is tobe transmittedMacMobileTerminalMAC AddressMAC address ofMobile TerminalMacNewAccessRouterMAC AddressMAC address ofnew access routerTimeIntervalTime in msecsPredicted Link_UPtime of linkConfidenceLevel%Link_UP levelpredicted atspecific timeUniqueEventIdentifierUse in eventrollbackoccurrence
A “Link_Event_Rollback” event is formed by combining the “Link_Going_Down” event with the “Link_Going_Up” event. The “Link_Event_Rollback” event is indicative of a trigger generated when it is expected that the “Link_UP” event or “Link_Down” event will not be generated any more within a specific time on the condition that the “Link_Going_Up” event or “Link_Going_Down” event are transmitted to a destination. A source of the “Link_Event_Rollback” event corresponds to a “Local MAC” and a “Remote MAC”. The following Table 7 shows parameters of the “Link_Event_Rollback” event.
TABLE 7NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource at whichevent occursEventDestinationEVENT_LAYER_TYPEDestination towhich event is tobe transmittedMacMobileTerminalMAC AddressMAC address ofMobile TerminalMacNewAccessRouterMAC AddressMAC address ofnew access routerUniqueEventIdentifierUse in eventrollbackoccurrence
A “Link_Available” event is indicative of an available state of a new specific link, and indicates the possibility of allowing a new base station (BS) or a new Point of Attachment (POA) to provide a link superior in quality as compared to a current BS or a current POA to which a current mobile terminal is connected. A source of the “Link_Available” event corresponds to a “Local MAC” and a “Remote MAC”. The following Table 8 shows parameters of the “Link_Available” event.
TABLE 8NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource at whichevent occursEventDestinationEVENT_LAYER_TYPEDestination to whichevent is to betransmittedMacMobileTerminalMAC AddressMAC address ofMobile TerminalMacNewAccessRouterMAC AddressMAC address ofnew access routerMacOldAccessRouterMAC AddressMAC address of oldaccess router
A “Link_Parameter_Change” event is indicative of an event generated when a change of a link parameter value is higher than a specific threshold level. The “Link_Parameter_Change” event includes link layer parameters, for example, a link speed (i.e., a link rate), a QoS (Quality of Service), and an encrypted value, etc. A source of the “Link_Parameter_Change” event corresponds to a “Local MAC” and a “Remote MAC”. The following Table 9 shows parameters of the “Link_Parameter_Change” event.
TABLE 9NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource atwhich eventoccursEventDestinationEVENT_LAYER_TYPEDestination towhich eventis to betransmittedMacMobileTerminalMAC AddressMAC addressof MobileTerminalMacAccessRouterMAC AddressMAC addressof new accessrouteroldValueOfLinkParameterOld value oflink parametersnewValueOfLinkParameterNew value oflink parameters
An information service (IS) provides detailed information associated with a network required for both network discovery and network selection, and must be designed to be freely accessed by a user over any network. The information service must include a variety of information components, for example, a link access parameter, a security mechanism, a neighborhood map, a location, information indicative of a service provider and other access information, and a link cost (i.e., cost of link).
FIG. 6 is a structural diagram illustrating a “Link Event” model and an “MIH Event” model. Referring to FIG. 6, the MIH event is indicative of an event transmitted from the MIH to either the upper management entity or the upper layer, and corresponds to conventional event triggers. The link event is indicative of an event transmitted from a lower layer (i.e., a MAC layer or a physical (PHY) layer) to the MIH, and uses primitives for use in individual interface MAC- or physical-layers.
FIG. 7 is a structural diagram illustrating a “Remote Link Event” model. Referring to FIG. 7, if a lower layer (MAC or PHY) contained in a local stack generates a link event and transmits the link event to the MIH contained in a local stack, the MIH of the local stack transmits the link event to the MIH of a remote stack.
FIG. 8 is a structural diagram illustrating a “Remote MIH Event” model. Referring to FIG. 8, the MIH function of the local stack generates a remote MIH event, and transmits the remote MIH event to a counterpart MIH function contained in a remote stack. The MIH function of the remote stack transmits the received event to an upper management entity or an upper layer contained in the remote stack. Similarly, the MIH function of the remote stack generates an event to the MIH function of the local stack, and the MIH function of the local stack transmits the aforementioned event to the upper layer of the local stack.
FIG. 9 is a structural diagram illustrating an “MIH command” model and a “Link command” model. Referring to FIG. 9, the MIH command is generated from the upper management entity or the upper layer, and is then transmitted to the MIH function, such that it commands the MIH to perform a specific task. The link command is generated from the MIH function, and is then transmitted to the lower layer, such that it commands the lower layer to perform a specific task.
FIG. 10 is a structural diagram illustrating a “Remote MIH command” model. Referring to FIG. 10, the remote MIH command is generated from the upper management entity or the upper layer, and is then transmitted to the MIH function. The MIH function transmits the received MIH command to a counterpart MIH function contained in a remote stack. Similarly, the upper layer contained in the remote stack generates a command and transmits the command to the MIH function of the remote stack, and the MIH function of the remote stack transmits the command to the MIH function of the local stack.
FIG. 11 is a structural diagram illustrating a “Remote Link Command” model. Referring to FIG. 11, the MIH function contained in the local stack generates a remote link command, and transmits the remote link command to a counterpart MIH function contained in a remote stack. The MIH function contained in the remote stack transmits the remote link command to a lower layer contained in the remote stack. Similarly, the MIH function contained in the remote stack generates a command, and transmits the command to the MIH function of the local stack, and the MIH function of the local stack transmits the command to the lower layer of the local stack.
FIG. 12 is a diagram illustrating operations of a mobile IPv4 system. Referring to FIG. 12, the mobile IPv4 additionally requires a variety of functions (i.e., a mobile host function, a home agent (HA) function, and a foreign agent (FA) function), such that it can provide the upper layer with clear mobility.
However, if a router or path is not optimized, there is no need for a correspondent node communicating with the mobile terminal to be changed to another. In this case, the mobile host is indicative of an IP host at which the mobility is supported. The home agent maintains location information associated with the mobile host, and serves as a router for performing tunneling of the mobile host. The foreign agent is indicative of a router for supporting the mobility over a foreign network.
Operations of the mobile IPv4 system shown in FIG. 12 will hereinafter be described. Referring to FIG. 12, the mobile host moves from its home network to a foreign network at step S111. The mobile host then receives an advertisement message currently broadcast over the foreign network, such that the mobile host recognizes that it has moved. Thereafter, the mobile host registers a temporary address or Care of Address (CoA) indicative of a current location of the mobile host in the home agent (HA) of the home network at step S112.
In this case, the temporary address (CoA) may be equal to an IP address (i.e., foreign agent (FA)-CoA) of the foreign agent, or may be equal to a co-located CoA, which is temporarily assigned to the mobile host via the DHCP in the foreign network.
Packets transmitted from an external part to the mobile host are transmitted to the home network. These packets are intercepted by the home agent recognizing the movement of the mobile terminal at step S113. The home agent having intercepted the above packets sets a destination address of the packets transmitted to the mobile host to an address of the foreign agent (FA) on the condition that the FA-CoA is used, encapsulates the destination address indicative of the FA address, and transmits the encapsulated address at step S114.
Thereafter, the encapsulated transmission packets are transmitted to the foreign agent (FA). The foreign agent (FA) then de-capsulates the received packets to recover original packets, and finally transmits the original packets to the mobile host at step S115.
Notably, packets transmitted from the mobile host to the correspondent host may be directly transmitted via the foreign agent (FA). If an ingress filtering problem occurs, the above-mentioned packets may also be transmitted via a reverse tunnel.
The principal functions required for the mobile IP are an agent discovery function, a registration function, and a routing function, for example, and their detailed description will hereinafter be described.
Agent discovery is indicative of a method for allowing a mobile terminal to determine whether the mobile terminal is connected to its own home network or a foreign network, such that the mobile terminal can recognize whether the mobile terminal itself has moved to another network.
A mobile IP extends a conventional ICMP (Internet Control Message Protocol) Router Discovery (i.e., IETF RFC 1256) to discover a desired agent. An agent advertisement message periodically broadcast by the agents (i.e., home agent, and foreign agent) includes a “Mobility Agent Advertisement Extension” message in an “ICMP Router Advertisement” message, and transmits the “ICMP Router Advertisement” message including the “Mobility Agent Advertisement Extension” message. An “Agent Solicitation” message transmitted when the mobile terminal searches for an agent employs the same method as in a conventional “ICMP Router Solicitation” message.
If the mobile terminal moves to another network, the registration function transmits current location information to the home agent, and allows the mobile terminal to receive services from the home network without any change.
The mobile IP provides two registration procedures, for example, FA-CoA and co-located CoA. If the mobile terminal uses the FA-CoA, the mobile terminal performs registration via the foreign agent (FA). If the mobile terminal uses the co-located CoA, the mobile terminal directly performs registration to the home agent.
The routing function defines a variety of functions required for properly routing a datagram transmitted/received to/from the mobile terminal when the mobile terminal is connected to or accesses a foreign network. The datagram includes a unicast packet, a multicast packet, and a broadcast packet.
DHCP operations will hereinafter be described. In order to correctly operate the DHCP, at least one DHCP server and a single DHCP client must be included in a corresponding network. Also, the network must further include not only the scope of a TCP/IP address but also a gateway address and a subnet mask. The DHCP client acquires the TCP/IP address information from the DHCP server while in operation. However, it should be noted that the acquired TCP/IP address is not permanent. The DHCP server provides a client with a lease address which may periodically expire or be periodically updated.
There are a plurality of client DHCP states, i.e., an initialization state (INT), a selecting state (SELECTING), a requesting state (REQUESTING), a binding state (BOUND), a renewing state (RENEWING), and a re-binding state (REBINDING), etc. The DHCP client acquires/maintains the lease address via a plurality of handshake steps, each of which is referred to as a state.
FIG. 13 is a flow chart illustrating operations of a DHCP client-server model, and shows a method for allowing the DHCP client to automatically receive an IP address from the DHCP server. Referring to FIG. 13, the client broadcasts a “DHCPDISCOVER” packet to peripheral servers at step S121. If individual servers receive the “DHCPDISCOVER” packet from the client, they answer the received “DHCPDISCOVER” packet and transmit a “DHCPOFFER” packet as a response signal at step S122.
The client receives the “DHCPOFFER” packet from one or more servers at step S122, selects one of the servers to request a configuration parameter, and broadcasts a “DHCPREQUEST” packet at step S123. In this case, servers not selected by the “DHCPREQUEST” packet recognize that the client has declined the offers of the servers.
The server selected by the “DHCPREQUEST” packet includes address configuration information in a “DHCPACK” packet, and transmits the “DHCPACK” packet with the address configuration information to the client as a response signal at step S124. If the client receives the “DHCPACK” packet from the selected server, the client constructs an address. However, if the client receives a “DHCPNAK” packet, the client re-starts the aforementioned process. Furthermore, the client may transmit a “DHCPRELEASE” packet to the server in order to return a leased address at step S125.
FIG. 14 is a flow chart illustrating operations of a mobile IPv6 system. Referring to FIG. 14, if the mobile node (MN) moves from a subnet A to another subnet B at step 0, the mobile node (MN) recognizes that the mobile node (MN) has moved to another subnet B using prefix information of a router advertisement (RA) message and a Neighbor Unreachable Detection (NUD) mechanism at step 1.
The mobile node (MN) alone acquires a temporary address (CoA) using the aforementioned address auto-configuration method at step 2. Thereafter, the mobile node (MN) transmits the “Binding Update (BU)” message, such that the home agent recognizes the acquired CoA at step 3.
The home agent (HA) having received the “BU” message combines (or binds) the home address of the mobile node (MN) with a temporary address (CoA), and transmits a “BACK” message as a response signal to the “BU” message at step 4.
The correspondent node (CN) firstly communicating with the mobile node (MN) does not recognize that the mobile node (MN) has moved to another subnet, such that it sets a destination address to a home address of the mobile node (MN), and transmits a resultant packet to the home agent (HA) at step 5.
The home agent (HA) for managing the mobile node (MN) then intercepts the packet of the correspondent node (CN), and performs tunneling of the packet to a current location of the mobile node (MN) at step 6. If the mobile node (MN) receives the tunneled packet, it determines that the correspondent node (CN) having transmitted the packet does not have the binding information, and transmits the “BU” message to the correspondent node (CN), such that it informs the correspondent node (CN) of a CoA of the mobile node (MN) at step 7.
The correspondent node (CN) having received the CoA of the mobile node (MN) stores the binding information, and directly communicates with the mobile node (MN) using the binding information at step 8.
FIG. 15 is a flow chart illustrating operations of the DHCPv6. Referring to FIG. 15, the client transmits a “SOLICIT” message to the “All_DHCP_Servers” address to recognize location information of a server at step (1). Individual DHCPv6 servers then output an “ADVERTISE” message including prefix information to answer the “SOLICIT” message at step (2).
Thereafter, the client selects one of the DHCPv6 servers, transmits a “REQUEST” message to the selected server, and at the same time requests an additional constituent parameter at step (3). The selected DHCPv6 server then outputs a “REPLY” message to answer the “REQUEST” message at step (4).
The client having received the “REPLY” message transmits a “RENEW” message to the DHCPv6 server, such that it updates conventional constituent parameters and the lifetime of allocated addresses, and starts operation of a T1 timer at step (5). In this case, the reference symbol “T1” is indicative of a specific time during which the client accesses the server having acquired an old address to increase the lifetime of a current address.
The DHCPv6 server then transmits another “REPLY” message as a response signal to the “RENEW” message at step (6). Finally, the client outputs a “RELEASE” message when an allocated address is no longer used, such that a corresponding address is released at step (7).
FIG. 16 is a flow chart illustrating a temporary address (CoA) re-setup procedure when a multi-mode mobile terminal is handed over from one interface network to another interface network. The multi-mode mobile terminal may use the mobile IPv4 system or the mobile IPv6 system to perform mobility management. The mobile IPv4 may use an FA-CoA or a co-located CoA as a temporary address (CoA). The mobile IPv6 may use a state-maintenance-type address or a non-state-maintenance-type address as a temporary address (CoA).
A method for re-establishing a temporary address (CoA) when a multi-mode mobile terminal is handed over to another interface network will hereinafter be described with reference to FIG. 16. First, the mobile terminal establishes a connection state with a link of a current interface network. If a high-quality link is detected from a MAC layer of a new interface network, the mobile terminal transmits the “Link_Avaialble” trigger signal to the MIH function.
The new MAC layer establishes a connection state with a new point of attachment (POA). If the new MAC layer establishes the connection state with the new POA, it performs an authentication process, and informs the MIH function of the mobile terminal and the MIH function of the new POA of the link setup state. The mobile terminal periodically receives an “Agent Advertisement” message of a foreign agent, such that it recognizes that a subnet has been changed to another subnet. The mobile terminal registers a temporary address (FA-CoA) in the home agent (HA).
Provided that a multi-mode mobile terminal is handed over from one subnet to another subnet in a current access interface network, or is handed over to another interface network, such that a subnet address is changed to another address, the mobile terminal must perform an IP temporary address (CoA) re-setup procedure. However, a multi-mode mobile terminal according to the conventional art has been designed to establish the aforementioned IP temporary address (CoA) re-setup procedure using only network layer information. Accordingly, a time delay during which the address is re-established is increased.